1. Field of the Invention
The invention relates to a method for dependably guiding a document in a document-processing device.
2. Description of the Related Art
A process for drawing in single-sheet paper in a printer is already known from DE 38 37 566 A1. On both sides of the print head mouth-piece there extends in the already known printer, a paper guide which can be moved together with the print head back and forth parallel to the platen. The single sheet to be printed is initially drawn into the printer, with the print head located outside the printing position, until its leading edge has just passed the printing station. Then, the print head is moved into the center of the printing region, so that the paper guide presses the paper against the printing roller. Only after this is complete is the paper brought to the line position to be printed.
In the case of the printing station known from DE 38 37 566 A1, the paper is guided around a platen, at which the normally flat paper is forced by the paper guide into a bowed shape. If is important that the paper be held closely against the platen in the region of the type line. After leaving this position, the paper resumes its flat shape. However, this presents a problem if, after leaving the printing station, the paper is to be directed by its leading edge into a paper channel, or after printing the lowest-possible line--is to be transported with its trailing edge ahead back into the feed channel. This is precisely the case with document or savings book printers, which are often designed as flat-bed printers. A flat-bed printer for the processing of document sections is known from Patent Abstracts of Japan, Volume 7, No. 271, M-260, abstract of JP, A, 58-151278.
In the case of these printers, the problem arises that non-flat documents are not satisfactorily transported and ejected. The problem is caused by the fact that, in the furthest drawn-in position, the document no longer lies with its edge, leading in the ejecting direction, in the ejecting channel and the directing or holding-down elements present there no longer influence the position of the document. This leading edge of an upwardly arched document strikes element of the ejecting channel, as a result of which creases (dog-ears) of the document are caused by the ejecting movement. It may also happen that the creased document gets caught in the ejecting channel and is torn. Outside document processing, deformations of the document occur for example due to improper storage of small document formats in the vertical position. The disadvantages which occur in the case of these printers are troublesome for the user. for example, the user must often reach into the unit to remove documents which have become caught.
Documents may also become deformed during the printing operation itself. This happens in particular in the case of needle printers which print documents in an unfavorable paper fiber direction. As a result of which--exacerbated by a low hardness of the clamping bar and under strong impact by the printing needles--a curving or arching up of the document is caused by the printing operation.